Entity Framework Core Projections

AstraFlow.Mapper.EntityFrameworkCore bridges IProjection<TSource, TDestination> and IParameterizedProjection<TSource, TDestination, TParameters> with EF Core relational providers so you can verify SQL translation across your entire projection catalog in unit and integration tests without executing queries against live rows.

Installation

Install AstraFlow.Mapper.EntityFrameworkCore in your persistence or integration test project (net10.0):

dotnet add package AstraFlow.Mapper.EntityFrameworkCore

Validating a Single Projection Translation

Call ValidateProjectionTranslation on any DbContext to compile the Select expression to relational SQL via .ToQueryString() without hitting the database:

using AstraFlow.Mapper.EntityFrameworkCore;

string sql = dbContext.ValidateProjectionTranslation(new OrderSummaryProjection());

For parameterized projections, pass a representative parameter object:

string parameterizedSql = dbContext.ValidateProjectionTranslation(
    new ActiveOfferProjection(),
    new PricingContext(0.10m, DateTimeOffset.UtcNow));

If any expression inside IProjection<,>.Expression cannot be translated by your configured EF Core database provider (such as PostgreSQL, SQL Server, or SQLite), EF Core throws a translation error immediately inside the validation call.

Validating All Registered Projections in CI

Run ValidateProjectionTranslations against your application's IProjectionRegistry in a single test to audit every projection across your solution:

using AstraFlow.Mapper;
using AstraFlow.Mapper.EntityFrameworkCore;
using AstraFlow.Assertions;

var parameterSamples = new Dictionary<Type, object>
{
    [typeof(PricingContext)] = new PricingContext(0.10m, DateTimeOffset.UtcNow)
};

EfCoreProjectionValidationReport report =
    dbContext.ValidateProjectionTranslations(projectionRegistry, parameterSamples);

report.HasFindings.Should().BeFalse();

Each finding inside EfCoreProjectionValidationReport reports:

• Missing sample parameter objects for parameterized projections so parameterizable queries are never silently skipped.
• Entities missing from the DbContext model or provider translation failures with the underlying EF Core exception detail.
• Source type, destination type, projection name (for named projections), and the active EF Core provider name.

Best Practices for Translatable Projections

• Keep projection expressions free of DI service calls, runtime IMapper.Map(...) invocations, and non-translatable C# helper methods.
• Avoid capturing mutable objects or complex service instances inside expression trees—pass scalar inputs explicitly via IParameterizedProjection<,,>.
• Keep raw Guid keys internal or transform identifiers after query materialization when public opaque IDs are required.

Related Guides

• Learn ProjectWith and parameterized projection authoring in Query Projections & Parameter Binding.
• Catch un-translatable query patterns before running tests in Build-Time Roslyn Analyzers.